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Parrot Virtual Machine bindings to libgit2

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README.md

Parrot Virtual Machine bindings to libgit2

This is library for Parrot Virtual Machine to provide libgit2 bindings to all languages running on Parrot Virtual Machine.

Build Status

Compiling

You need Parrot VM 3.5.0 or higher configured with libffi to compile parrot-libgit2 . 5.3.0 or higher is recommended.

To see if your Parrot has libffi

parrot_config HAS_LIBFFI

You should see a true value. If you see a 0 or empty string, your Parrot is not configured with libffi.

The language Winxed is included in Parrot >= 3.5.0, and the build system of parrot-libgit2 uses it. To build parrot-libgit2:

winxed setup.winxed build

Installation

sudo winxed setup.winxed install

For now, also copy libparrotgit.so to your lib folder manually.

Running Tests

parrot-libgit2 uses Rosella to run and implement a test suite.

To run the parrot-libgit2 test suite:

winxed setup.winxed test

Cleaning up

winxed setup.winxed clean

Theory

We read in libgit2 header files and generate an NCI binding file. This file is read in by $PARROT/tools/dev/ncidef2pir.pl and a PIR file is generated which allows Parrot to call libgit2 C functions from PIR.

This only understands function signature API changes, not datastructure API changes. Those are still manually decribed by the StructView PMC in src/Git2/Common.winxed .

This makes it trivial to release a new version of parrot-libgit2 when the libgit2 API changes, which it will for the forseable future. Currently, the 0.19.0 release of libgit2 is supported.

By default, a low-level PIR binding is created for every libgit2 API function, so every release of parrot-libgit2 supports all of libgit2. In addition to this, a few stubborn humans are implementing a higher-level and object-oriented interface in the Winxed programming language (which comes bundled with Parrot since 3.5.0).

A simplistic C wrapper exists for some functions that cannot be called directly from winxed. These functions are present in src/parrotgit.c. These are compiled to a shared library called libparrotgit.so.

Generating NCI definitions

There is a script called header2nci.pl in bin/ that generates the NCI definition file from a libgit2 header file. Example:

perl ./bin/header2nci.pl /usr/local/include/git2/repository.h

This script has some bugs and does not parse all of libgit2 correctly yet. TODO: Make header2nci.pl able to parse all libgit2 headers.

NCI defs are automatically generated during setup.

How to use the high-level Winxed bindings:

These are small snippets of code that show how the high level bindings to Winxed can be used. The bindings are basically wrappers around the plumbing functions provided by libgit2 and don't contain much porcelain stuff, though that can be built around these bindings. Chapter 9 of Pro Git is a good reference for git internals.

Opening a repository:

using Git2.Repository;
var repo = new Git2.Repository("/path/to/repository");
...
repo.free();

Creating a repository:

using Git2.Repository;
var repo = new Git2.Repository;
repo.init("/path/to/repository");
repo.free();

Cloning a repository:

using Git2.Repository;
var repo = new Git2.Repository;
repo.clone("https://github.com/letolabs/parrot-libgit2.git", "/tmp/parrot-libgit2");
repo.free();

Using the index:

using Git2.Repository;
using Git2.Index;

var repo = new Git2.Repository("/path/to/repository");
var git_index = new Git2.Index();

git_index.set_index(repo.ptr);
int ecount = git_index.get_entrycount();
print("Index entry count" + ecount + "\n");

git_index.free();
repo.free();

Getting config variables:

using Git2.Config;
var config = new Git2.Config;
config.get_config("path/to/repo/config");

int cfg_val = config.get_int32("help.autocorrect");
print(cfg_val);

Getting an object from SHA1 hash:

using Git2.Oid;

var git_oid = new Git2.Oid();
var hex = "599955586da1c3ad514f3e65f1081d2012ec862d";

git_oid.oid_from_str(hex);

Getting Commit Data:

using Git2.Commit;
using Git2.Repository;
using Git2.Oid;

var repo = new Git2.Repository(".");

var hex = "e1380b1f60babf677921c4a9b5e92acda0b15e18";
var git_oid = new Git2.Oid();
git_oid.oid_from_str(hex);

var commit1 = new Git2.Commit();
commit1.commit_lookup(repo, git_oid);

int ctime = commit1.commit_time();
int parentcount = commit1.parentcount();

commit1.free();
repo.free()

Dealing with references:

using Git2.Repository;
using Git2.Reference;
var repo = new Git2.Repository(".");
var name = "HEAD";

var ref = new Git2.Reference(repo, name);
int type = ref.reference_type();
string ref_name = ref.reference_symbolic_target();

Revision Walking: You can traverse the DAG(Directed Acyclic Graph) created by the parent pointers.

using Git2.RevWalk;
using Git2.Repository;
using Git2.Oid;
using Git2.Commit;

var repo = new Git2.Repository(".");

var hex = "e1380b1f60babf677921c4a9b5e92acda0b15e18";
var git_oid = new Git2.Oid();
git_oid.oid_from_str(hex);

var rev_walk = new RevWalk;
rev_walk.init(repo);
rev_walk.push(git_oid);

while(rev_walk.next() == 0){
    var commit1 = new Git2.Commit();
    commit1.commit_lookup(repo, rev_walk.oid);
    int parentcount = commit1.parentcount();
    print(parentcount + " ");
    commit1.free();
}
rev_walk.free();
repo.free();

Blobs:

using Git2.Repository;
using Git2.Oid;
using Git2.Blob;

var repo = new Git2.Repository(".");

var hex = "a556bfd051e6cd09844eda9ccb372f37629f5385";
var git_oid = new Git2.Oid();
git_oid.oid_from_str(hex);

var blob = new Blob;
blob.lookup(repo, git_oid);

var size = blob.raw_size();
print(size);
blob.free();
repo.free();

Trees and TreeIndex:

using Git2.Tree;
using Git2.TreeIndex;
using Git2.Repository;

var repo = new Git2.Repository(".");
var tree = new Git2.Tree();
var oid = new Git2.Oid();
var hex = "556d8f5741abf8728fce8cdb0e1f764bce7dc8a2";
oid.oid_from_str(hex);
tree.lookup(repo, oid);

int count = tree.entrycount();

var entry = new Git2.TreeIndex();
entry.byindex(tree, 0);
string name = entry.name();

Contributing

Beer, pull requests and patches welcome! Fork and be merry.

License

GPLv3. See the LICENSE file for details.

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